Transporter associated with Antigen Processing molecules (TAP1 and TAP2) mediate the transfer of cytosolic peptides into the lumen of the endoplasmic reticulum for association with newly synthesized class I molecules of the Major Histocompatibility Complex (MHC). Molecular and functional analysis of the rat and human TAP2 homologues indicated major differences in gene diversification patterns and selectivity of peptides transported. This study analyzes the alleles of the gorilla TAP2 locus to determine if the pattern of diversification resembled either of those two species. Sequence analysis of the TAP2 cDNAs from gorilla EBV-transformed B-cell lines revealed four alleles with a genetic distance of less than 1%. The nucleotide substitutions, distinguishing the alleles, are confined to the 3'-half of the coding region, and occur individually or within two small clusters of variability. Diversification of the locus appeared to have resulted from point substitutions and recombinational events. Evolutionary rate estimates for the TAP2 gene in gorilla and human closely approximate those observed for other hominoid genes. The amino acid polymorphisms within the gorilla molecules are distinct from those present in the human homologues. The absence of ancestral polymorphisms suggests that the gorilla and human TAP2 genes have not evolved in a trans-species fashion, in contrast to the class I and II MHC genes, but rather diversification has occurred since the divergence of the lineages. Key Words MHC, Gorilla, TAP